A cured substance by using an epoxy resin and other additives exhibits generally the excellent thermal, mechanical, electrical properties and the adhesion property, and therefore, it has been used widely in various industry.
Particular, a molding material in which an epoxy resin and various fillers are combined has been used widely as an adhesion or insulation material of an electronics or electrical machine or a construction material, and it plays an important part in satisfying a demand of the miniaturization of the installation, and an improvement of the reliability and the productivity.
Recently, in the electric and electronic field and the field of the transport machine such as an airplane and a motor, the material having more better heat resistance has been required due to high performance, miniaturization and light weight of machine, and with the steady growth of a semiconductor industry, the package element for protecting the semiconductor element from the moisture and the impact from outside has been investigated. Generally, there are two package modes; one includes the use of ceramic or metal and the other includes the use of the epoxy resin or the silicone resin.
However, the plastic package mode using the epoxy resin has been mainly used in view of the productivity and cost.
Meanwhile, recently, since the size of semiconductor chip is increased and the width of wiring is narrowed with the high integration, the improvement of the heat resistance and the moisture resistance has been required in order to reduce the heat stress caused in using the product and to improve reflow property.
In particular, according to the trend of surface mounting technology since in the semiconductor chip the package should be withstand the soldering process which is effected at the high temperature above 215.degree. C. in contrast with DIP (Dual In-line Package) mode of the prior art, the need on the heat resistance has been increased.
In the light of these requirements, although the epoxy resin of the prior art has the excellent mechanical and electrical properties and it has advantages in view of the productivity and cost, it does not have the sufficient heat resistance.
As a method overcoming these problems, there is a method which uses polyimide resin having an excellent heat resistance instead of an epoxy resin. However, in the method, it is difficult to mold polyimide resin due to its infusibility and the polyimide resin is unpractical in cost. Also, polymaleimide represented by N,N'-4,4'-diphenylmethane bismaleimide having high heat stability requires the conditions of long time and high temperature for the complete curing.
Meanwhile, Japanese Laid-open Patent Publication No. (Sho) 48-67395, 54-142298, 62-35410, 62-195015, 62-53324, 62-212419, 62-270618 and 63-37118 and J. Macromol, Sci. Chem. A22(8), PP 1101.about.1107(1985) disclose that the thermal property of the resin composition is improved by curing the epoxy resin by a reaction initiator having a functional group such as --COOH, --OH, and --NH in the terminal of imide backbone. However, in this method, there is a limitation in increasing the amount of imide contributing to the improvement of heat resistance.
As another method, there is a method in which a prepolymer is prepared by reacting a substance having an amino group such as aminophenol or diaminodiphenylmethane in its terminal with the available maleimides, and thereafter, the remaining amino groups are reacted with the epoxy groups in the resin composition by adding the prepolymer in the resin composition [See: Japanese Laid-open Patent Publication No. (Sho) 58-215452, 58-89619, 59-64660, 59-227924, 62-227917, U.S. Pat. No. 4,288,359 and J. Appl. Polym. Sci. Vol 21, PP 809.about.820(1977)]. However, in this case, it is difficult to control the degree of reaction and the weight of imide should be limited.
Also, a method which enhances a heat resistance of a cured product by improving a curing property by combining an epoxy resin and an amine compound in polyfunctional polymaleimide has the problems on a storage stability at room temperature (20.degree. C..about.30.degree. C.) and an uniform curing reaction.
Further, in order to increasing a glass transition temperature of an element for a plastic package, Japanese Laid-open Patent Publication No. (Sho) 54-142298 and 58-215452 proposed a resin composition using an aromatic imide compound. However, the resin composition for a semiconductor using the aromatic imide compound has low compatibility between it and the epoxy resin and low moldability, and therefore, it has many problems on the improvement of performance.
Accordingly, the purpose of the present invention is to provide a new modified epoxy resin to be modified by maleimide to be added in a heat-resistant resin composition in order to improve a thermal property and a method for the preparation thereof.
The other purpose of the present invention is to provide a resin composition for sealing a semiconductor element having the excellent heat resistance and moldability by using the modified epoxy resin to be modified by the maleimide in a resin composition for sealing an element for a plastic package.